This invention relates to a process for producing a base board having solder-filled semicircular through-holes at side walls.
Printed wiring boards have been produced, as shown in FIG. 7, by placing a base board (or a chip carrier) 3 mounting electronic parts and having a plurality of semicircular through-holes 5 at side walls on lands (or pads) 2 on a printed circuit board 1 and bonding the through-hole portions to the lands by using solder 7. The base board 3 is prepared by forming through-holes 10 in a base sheet 9 as shown in FIG. 5, and cutting the base sheet at a predetermined portion to give a plurality of base boards as shown in FIG. 6 with a predetermined size. The semicircular through-holes 5 at side walls 4 are obtained by forming round through-holes 10 in the base sheet 9, covering each through-hole wall with a copper coating 12 formed by electroless plating, and cutting the base sheet 9 with a cutter along the line 15 (FIG. 5).
But there often take place partial peeling 16 of the copper coating 12 at edge portions of semicircular through-holes 5 and cracks 17 at the inner wall of the semicircular through-holes 5 at the time of cutting, which results in damaging the reliability. Further, since the volume of solder 7 used for soldering the base board 3 to the printed circuit board 1 is small, there arises a problem due to a lack in the reliability.